Motor And Oil Cooling Cycle; Vfd Cooling Cycle - Carrier AquaEdge 19XR Start-Up, Operation And Maintenance Instructions Manual

MOTOR AND OIL COOLING CYCLE

The motor and the lubricating oil are cooled by liquid refrigerant
taken from the bottom of the condenser vessel (Fig. 8 and 9). Re-
frigerant flow is maintained by the pressure differential that ex-
ists due to compressor operation. After the refrigerant flows past
an isolation valve, an in-line filter, and a sight glass/moisture in-
dicator, the flow is split between the motor cooling and oil cool-
ing systems.
CAUTION
To avoid adverse effects on chiller operation, consideration
must be made to condenser water temperature control. For
steady state operation, the minimum operating refrigerant
pressure differential between cooler and condenser is ap-
proximately 20 psi (138 kPa) with a maximum evaporator
refrigerant temperature of 65°F (18°C). Consult Chiller
Builder for required steady state operational limits. Invert-
ed start conditions are acceptable for short durations of
time, but for periods exceeding 5 minutes, a special control
solution strategy should be used to allow the chiller to es-
tablish a minimum refrigerant pressure differential, and
thereby adequate equipment cooling.
Flow to the motor cooling system passes through an orifice and
into the motor. Once past the orifice, the refrigerant is directed
over the motor by spray nozzles. The refrigerant collects in the
Fig. 7 — Refrigeration Cycle — 19XR(V) Two-Stage Compressor
bottom of the motor casing and is then drained back into the
cooler through the motor refrigerant drain line. An orifice (in
the motor shell) maintains a higher pressure in the motor shell
than in the cooler. The motor is protected by a temperature sen-
sor embedded in the stator windings. An increase in motor
winding temperature past the motor override set point over-
rides the temperature capacity control to hold, and if the motor
temperature rises 10F (5.5C) above this set point, the con-
trols close the inlet guide vanes. If the temperature rises above
safety limit, the compressor shuts down.
Refrigerant that flows to the oil cooling system is regulated by
expansion valves. The expansion valves regulate flow into the
oil/refrigerant plate and frame-type heat exchanger (the oil
cooler in Fig. 8), and control oil temperature to the bearings.
The refrigerant leaving the oil cooler heat exchanger returns to
the chiller cooler.

VFD Cooling Cycle

If equipped with a refrigerant-cooled unit-mounted VFD, the
refrigerant line that feeds the motor cooling and oil cooler also
feeds the heat exchanger on the unit-mounted VFD. Refriger-
ant is metered through an orifice as refrigerant is leaving the
VFD heat exchanger. The refrigerant leaving the heat exchang-
er returns to the cooler. Alternatively, if equipped with an air-
cooled unit-mounted VFD the cooling of the VFD is integral to
the VFD by means of cooling with ambient air.
12